The present invention relates to magnetic tape cassettes, and more particularly to an improved magnetic tape cassette which is substantially equal in size to a Philips-type magnetic tape cassette.
Recently, cassette tape recorders have been reduced both in size and in weight. Accordingly, there has been a strong demand for magnetic tape cassettes suitable for high-quality and high-density signal recording and reproduction and which have long playing times.
Heretofore, signal recording and reproducing operations with compact magnetic tape cassettes generally employed for audio devices have been carried out in an analog mode using analog signals. However, with analog recording techniques, high-density signal recording and reproducing with compact magnetic tape cassettes are limited. On the other hand, it is well known in the art that a digital system such as pulse code modulation (PCM) in which signal recording and reproducing operations are carried out with input signals converted into pulse signals permits high-density signal recording and reproduction without adverse effects due to noise in the signal transmission paths and the quality of the recording medium employed.
Recently a magnetic head has been developed which permits high-density signal recording and reproducing as in multi-track signal recording and reproducing on a magnetic tape which is sufficiently small in width that it can be used in a Philips-type magnetic tape cassette. As a result, it is possible to perform a multi-track signal recording and reproducing operation with a compact magnetic tape cassette which is substantially equal in size to the Philips-type magnetic tape cassette.
For thirty-six track recording with the above-described compact magnetic tape cassette using such a stationary head, the width of each track is of the order of 100 microns, which is much smaller than that of each track in a conventional four-track recording operation with an ordinary Philips-type cassette. Due to the small head and track width, if dust from the magnetic tape becomes lodged in the magnetic head, the recorded information is much more adversely affected in recording and reproducing characteristics than in the conventional operation.
An example of a magnetic tape cassette suitable for recording and reproducing signals with a high density is a video tape cassette, which is ordinarily recorded on and reproduced using a rotary head system. In order to successfully use a video tape cassette to perform high-density signal recording, it is essential that the magnetic tape be protected from damage and from the effects of dust. For this purpose, the cassette includes a swingable guard panel to open and close the opening which is formed in the front end wall of the cassette body. In the rotary head system, the magnetic tape in the cassette (except for special cassettes) is run in only one direction for recording or reproducing signals, and therefore it is unnecessary, as in a magnetic tape cassette permitting the use of both sides (A and B sides), for both sides of the cassette to be symmetrical in construction. Furthermore, in the rotary head system, in general, two magnetic heads inclined with respect to the tape running direction and alternately brought into contact with the magnetic tape while being rotated, which has the effect of sweeping off dust. Therefore, there is a smaller likelihood that will effect the signal recording and reproducing characteristics compared with that in the case of the stationary system.
The technical concept of the invention is applied to a magnetic tape cassette which, like a Philips-type magnetic tape cassette, is recorded on and reproduced using a stationary head system, and which has a number of recording tracks and permits the use of the upper and lower halves of the magnetic tape for recording or reproducing signals, i.e., the use of both sides (A and B sides) thereof. Such a cassette, due to the use of a stationary head system, is more likely to be affected in signal recording and reproducing characteristics by dust than when a rotary head system is employed. Accordingly, the cassette needs a guard panel which provides an improved dust-proofing effect than the type of guard panel employed with an ordinary video tape cassette.
In general, as a magnetic tape cassette is miniaturized, the cassette body and the guard panel thereof cannot necessarily be reduced in wall thickness, as a result of which they are more likely to be deformed by an external force. Especially, the guard panel which opens and closes the opening formed in the front end wall of the cassette body should have a structure that permits positive closure of the opening and prevents unwanted movement of the guard panel.